Proper ventilating of the crankcase of an internal combustion engine is important in order to effect separation of oil from the blow-by gases and thereby significantly reduce oil loss and contamination; and to prevent unfiltered air from being drawn in past the seals, gaskets and the like when the crankcase is subjected to periods of depression. Prior systems have heretofore been proposed in an attempt to overcome these problems; however, such systems have been beset with one or more of the following shortcomings: (a) the system is of complex and costly construction; (b) it is difficult to service and maintain; and (c) it is inefficient in operation.